How DO they actually locate earthquakes?
Alternatives to S-P TriangulationHubenthal, M. Taber, M.
An Inverse Problem
• We know the end product; arrival times • We have a velocity model for Earth and • we want to calculate the original event– Location– Origin time
Forward Problem = Model parameters → Data
Inverse Problem = Data → Model parameters
The bisector method• P arrivals are
much easier to pick
• Assumes an extremely simple velocity model
Which station of this record section was closest?
1
2
3
4
5
6
Bisector Steps
1. Mark and measure path between TATO/WAKE2. Find midpoint of path3. Draw bisector perpendicular to path4. Label Bisector with station names5. Determine which side of the bisector was close to
the event.6. Repeat with TATO/YAK7. Repeat with WAKE/YAK8. Repeat with additional stations of your choice
Path
Bisector
TATO
WAK
E
X
Bisector Steps
1. Mark and measure path between TATO/WAKE2. Find midpoint of path3. Draw bisector perpendicular to path4. Label Bisector with station names5. Determine which side of the bisector was close to
the event.6. Repeat with TATO/YAK7. Repeat with WAKE/YAK8. Repeat with additional stations of your choice
Solution
Compare to regional seismicity
Earth is ComplexPREM Model
Earth is ComplexPREM Model
Solution to complexity
• Iterative approach – Solution through the model provides result – Result is run back through the model to see if it
matches the observations (forward problem)– Differences used to refine the model to compute
a new solution. – Process continues until some condition is met
In reality
• More data• More complex models• Iterative approach